1. Field of The Invention
The present invention relates to a driving circuit of a stepping motor for a floppy disk drive, and more partricularly to a driving circuit of a stepping motor which is capable of saving the consumption of electricity by cutoff of the driving electric current to the stepping motor and the driver at the standby for carriage feeding or after head seek.
2. Description of The Prior Art
The floppy disk drive has been widely used for external storage of the computer, and specifically in recent years practically used is the small sized device utilizing 3.5 inch or 3 inch micro floppy disk media, which is applied for the portable computers. In order to design such small sized or portable devices there is problem on the electric current consumption of the floppy disk drive itself. Specifically in the portable computer, decrease of the electric current consumption is strongly requested since the battery drive is required in the normal cases.
The electric current consumption of the floppy disk drive is occupied in its major part by the stepping motor which feeds or positions the carriage to a predetermined place and by the driver attached to the stepping motor, and the power saving of the electricity in these elements effects the total electric current consumption of the device.
In ordinary cases, it was generally thought that the hold current was necessary for the stepping motor at the standby or after the head seek as well as at the seek time so that the head can be positioned at the correct track. In recent years, however, the improvement of the stepping motor clarifies that the hold current is not always necessary at the standby and after the head seek, and it is offered that the electric current for the stepping motor be cut off at the standby and after the head seek by off-operation of the power saving switch.
In FIG. 3 shown therein is a power saving circuit in prior art. Feeding control signals are supplied from a driver 12 to a stepping motor 10, and action of the driver 12 is controlled by the feeding control signals supplied from a control circuit 14.
In the prior art device, it is composed as the electric current consumption in the stepping motor 10 and the driver 12 can be decreased by cutoff of the current flow from the power source (Vcc) to the driver 12 by a power saving switch 16 at the standby and after the head seek.
However, although the prior art device mentioned above takes preferable power saving action, on the other hand, at the time of head seek there occurs loss in the drive voltage, which becomes great problem specifically in the low voltage drive by the battery. In other words, at the seek time the control circuit 14 puts the transister 16 of economy switch in the on-operation state, but the transister 16 has saturation voltage between emitter and collector, and the portion of this saturation voltage causes in the voltage loss.
Therefore, in the prior art device, in order to obtain the high voltage enough to cover the voltage loss in the case of battery drive, some kinds of means are required, a DC/DC convertor or the like for example, which makes the device get larger on the contrary, and there occurs another problem that relatively major amount of the electric current is wasted in the convertor.